1. Field of the Invention
This invention concerns chemical mechanical polishing slurries that are useful when used in sequence for polishing a substrate including a copper portion and a tantalum portion. The invention includes a first chemical mechanical polishing slurry including an abrasive, an oxidizing agent, a complexing agent and at least one organic amino compound. The invention also includes a second chemical mechanical polishing slurry including an abrasive, an oxidizing agent and a complexing agent where the weight ratio of oxidizing agent to complexing agent is greater than 15. This invention also includes a method for using the first and second chemical mechanical polishing slurries to sequentially polish a substrate including a copper portion and a tantalum portion.
2. Description of the Art
Integrated circuits are made up of millions of active devices formed in or on a silicon substrate. The active devices, which are initially isolated from one another, are interconnected to form functional circuits and components. The devices are interconnected through the use of multilevel interconnections. Interconnection structures normally have a first layer of metallization, an interconnection layer, a second level of metallization, and sometimes a third and subsequent level of metallization. Interlevel dielectrics such as doped and undoped silicon dioxide (SiO.sub.2), or low-k dielectrics tantalum nitride are used to electrically isolate the different levels of metallization in a silicon substrate or well. The electrical connections between different interconnection levels are made through the use of metallized vias. U.S. Pat. No. 5,741,626, which is incorporated herein by reference, describes a method for preparing dielectric tantalum nitride layers.
In a similar manner, metal contacts are used to form electrical connections between interconnection levels and devices formed in a well. The metal vias and contacts may be filled with various metals and alloys including titanium (Ti), titanium nitride (TiN), tantalum (Ta), aluminum copper (Al--Cu), aluminum silicon (Al--Si), copper (Cu), tungsten (W), and combinations thereof. The metal vias and contacts generally employ an adhesion layer such as titanium nitride (TiN), titanium (Ti), Tantalum (Ta), Tantalum nitride (TaN) or combinations thereof to adhere the metal layer to the SiO.sub.2 substrate. At the contact level, the adhesion layer acts as a diffusion barrier to prevent the filled metal and SiO.sub.2 from reacting.
In one semiconductor manufacturing process, metallized vias or contacts are formed by a blanket metal deposition followed by a chemical mechanical polish (CMP) step. In a typical process, via holes are etched through an interlevel dielectric (ILD) to interconnection lines or to a semiconductor substrate. Next, a thin adhesion layer such as tantalum nitride and/or tantalum is generally formed over the ILD and is directed into the etched via hole. Then, a metal film is blanket deposited over the adhesion layer and into the via hole. Deposition is continued until the via hole is filled with the blanket deposited metal. Finally, the excess metal is removed by chemical mechanical polishing, (CMP) to form metal vias. Processes for manufacturing and/or CMP of vias are disclosed in U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.
In a typical chemical mechanical polishing process, the substrate is placed in direct contact with a rotating polishing pad. A carrier applies pressure against the backside of the substrate. During the polishing process, the pad and table are rotated while a downward force is maintained against the substrate back. An abrasive and chemically reactive solution, commonly referred to as a "slurry" is applied to the pad during polishing. The slurry initiates the polishing process by chemically reacting with the film being polished. The polishing process is facilitated by the rotational movement of the pad relative to the substrate as slurry is provided to the wafer/pad interface. Polishing is continued in this manner until the desired film on the insulator is removed. The slurry composition is an important factor in the CMP step. Depending on the choice of the oxidizing agent, the abrasive, and other useful additives, the polishing slurry can be tailored to provide effective polishing to metal layers at desired polishing rates while minimizing surface imperfections, defects and corrosion and erosion. Furthermore, the polishing slurry may be used to provide controlled polishing selectivities to other thin-film materials used in current integrated circuit technology such as titanium, titanium nitride, tantalum, tantalum nitride, and the like.
Typically CMP polishing slurries contain an abrasive material, such as silica or alumina, suspended in an oxidizing, aqueous medium. For example, U.S. Pat. No. 5,244,534 to Yu et al. reports a slurry containing alumina, hydrogen peroxide, and either potassium or ammonium hydroxide that is useful to remove tungsten at predictable rates with little removal of the underlying insulating layer. U.S. Pat. No. 5,209,816 to Yu et al. discloses a slurry comprising perchloric acid, hydrogen peroxide and a solid abrasive material in an aqueous medium that is useful for polishing aluminum. U.S. Pat. No. 5,340,370 to Cadien and Feller discloses a tungsten polishing slurry comprising approximately 0.1 M potassium ferricyanide, approximately 5 weight percent silica and potassium acetate. Acetic acid is added to buffer the pH at approximately 3.5.
U.S. Pat. No. 4,789,648 to Beyer et al. discloses a slurry formulation using alumina abrasives in conjunction with sulfuric, nitric, and acetic acids and deionized water. U.S. Pat. Nos. 5,391,258 and 5,476,606 disclose slurries for polishing a composite of metal and silica which includes an aqueous medium, abrasive particles and an anion which controls the rate of silica removal. Other polishing slurries for use in CMP applications are described in U.S. Pat. No. 5,527,423 to Neville et al., U.S. Pat. No. 5,354,490 to Yu et al., U.S. Pat. No. 5,340,370 to Cadien et al., U.S. Pat. No. 5,209,816 to Yu et al., U.S. Pat. No. 5,157,876 to Medellin, U.S. Pat. No. 5,137,544 to Medellin, and U.S. Pat. No. 4,956,313 to Cote et al.
There are various mechanisms disclosed in the prior art by which metal surfaces can be polished with slurries. The metal surface may be polished using a slurry in which a surface film is not formed in which case the process proceeds by mechanical removal of metal particles and their dissolution in the slurry. In such a mechanism, the chemical dissolution rate should be slow in order to avoid wet etching. A more preferred mechanism is, however, one where a thin abradable layer is continuously formed by reaction between the metal surface and one or more components in the slurry such as a complexing agent and/or a film forming layer. The thin abradable layer is then removed in a controlled manner by mechanical action. Once the mechanical polishing process has stopped a thin passive film remains on the surface and controls the wet etching process. Controlling the chemical mechanical polishing process is much easier when a CMP slurry polishes using this mechanism.
Current copper containing substrates that are polished using chemical mechanical polishing also use Ta and TaN adhesion layers. Ta and TaN are chemically very passive and mechanically very hard and thus difficult to remove by polishing. The use of a single slurry, which performs with a high Cu:Ta selectivity demand prolonged polishing times for Ta, i.e. a significant overpolishing times for copper, during which there is a significant degradation of dishing and erosion performance.
Several relevant Cu chemistries have been discussed in the open literature, each failing to deliver a process which successfully addresses all of the key requirements of a chemical-mechanical polishing slurry useful for a substrate including both copper and tantalum. As a result, there is a need for one or more CMP slurries that can be used successfully to polish copper and tantalum containing substrates.